Crystal
structure prediction of organic pigments: quinacridone as an example
Panina N (Panina, N.), Leusen FJJ (Leusen, F. J. J.), Janssen FFBJ
(Janssen, F. F. B. J.), Verwer P (Verwer, P.), Meekes H (Meekes, H.),
Vlieg E (Vlieg, E.), Deroover G (Deroover, G.)
J. Appl. Cryst. 40 (2007) 105-114
Abstract:
The structures of the alpha, beta and gamma polymorphs of quinacridone
( Pigment Violet 19) were predicted using Polymorph Predictor software
in combination with X-ray powder diffraction patterns of limited
quality. After generation and energy minimization of the possible
structures, their powder patterns were compared with the experimental
ones. On this basis, candidate structures for the polymorphs were
chosen from the list of all structures. Rietveld refinement was used to
validate the choice of structures. The predicted structure of the gamma
polymorph is in accordance with the experimental structure published
previously. Three possible structures for the beta polymorph are
proposed on the basis of X-ray powder patterns comparison. It is shown
that the alpha structure in the Cambridge Structural Database is likely
to be in error, and a new alpha structure is proposed. The present work
demonstrates a method to obtain crystal structures of industrially
important pigments when only a low-quality X-ray powder diffraction
pattern is available.